When adding a time-dependent covariate to my DTSMA model, most of my data is excluded from the analysis since the censored subjects have missing data for the covariate after being censored.

In a search of past topics it was suggested that if the covariate is mentioned in the model statement that it will include those with missing values. However, when I try this, it says the time-dependent part of the model statement is invalid. I'm not sure if I'm doing the model incorrectly or the coding.